And now the authorities have a new enemy on their hands: the feared marbled crayfish – the only known decapod crustacean with the ability to reproduce through parthenogenesis, also known as self-fertilisation.

Until now, the marble crayfish has kept south of the Danish border, but in late January one was discovered in Karup Stream near Skive in Jutland.

Authorities investigating
Aside from being able to reproduce in great numbers and displace the naturally-occurring crayfish in Denmark, the new invader can carry crayfish plague, which can seriously damage local flora and fauna.

“It’s illegal to release the marble crayfish into nature, but unfortunately there are some who do so. It’s probably also how the ones found in Skive ended up there,” said Josefine Møller, a biologist with the Danish environmental protection agency, Miljøstyrelsen.

Miljøstyrelsen intends to investigate whether the marble crayfish found was a one-off individual or if it came from a larger population.